Fluoropolymer low reflecting layers for plastic lenses and devices

ABSTRACT

A one or two layer coating system has been developed for plastic substrates. The one coating system low reflective layer consists of a fluorinated copolymer having the formula: VF2/TFE/HFP, VF2/HFP or VF2/TFE/PMVE. In the two coating system, the upper coating layer consists of TFE/HFP, VF 2 /TFE/HFP, or TFE/Perfluorodioxole, and the lower coating layer consists of VF 2 /TFE/HFP, VF/TFE/HFP, VAc/TFE/HFIB, or TFE graft to PVOH.

FIELD OF INVENTION

The present invention relates to fluoropolymer coated plastics. Morespecifically, it relates to fluoropolymer coated plastics having goodadhesion, low reflective properties, and water and oil repellency.

TECHNICAL BACKGROUND

Much work has been done concerning low reflective plastics, particularlyfor plastic lenses and optical devices. One method used is vapordisposition of oxidized metal on the surface of the plastic. However,this method uses a batch process and when the substrate is large, theproductivity becomes low. Another way is to apply a coating offluoropolymer solutions. The coating is done by a dipping process and isapplicable for large substrates with high productivity. Thoughfluoropolymers have low reflective indexes, they also have very pooradhesion with plastic substrates. Improvement in the adhesion betweenfluoropolymers and substrate plastics has been long sought. The purposeof this invention is to provide the technology for low reflective indexand good adhesion using fluoropolymer solutions.

SUMMARY OF THE INVENTION

The one layer coating system provided by the present invention consistsof a fluorinated copolymer having the formula:

VF₂/TFE/HFP

wherein the molar ratio of Tetrafluoroethylene (TFE) toHexafluoropropylene (HFP) is between 0.1 and 1.9, and the VF₂ content is12 to 60 mole %. Preferably the VF₂ content is 12 to 50 mole % for PMMAsubstrates and 18 to 50 mole % for PC, PET, and PS substrates. Morepreferred is where the molar ratio of TFE to HFP is between 0.9 and 1.9,and the VF₂ content is preferably 12 to 50 mole % forPolymethylmethacrylate (PMMA) substrates and 18 to 50 mole % forPolycarbonate (PC), Polyethyleneterephthalate (PET), and Polysulfone(PS) substrates.

Also preferred is where the VF₂ content is greater than 50 mole % to 60mole %; more preferred is where the substrate is PMMA, PC, PET or glass.

A one layer coating system is also provided by the present inventioncomprising a fluorinated copolymer having the formula

VF₂/HFP

wherein the VF₂ content is about 40-80 mole %. Preferably, the VF₂content is about 40-50 mole % and the substrate is PMMA. Alsopreferably, the VF₂ content is about 70-80 mole % and the substrate isglass.

A one layer coating system is also provided by the present inventioncomprising a fluorinated copolymer having the formula

VF₂/TFE/PMVE

wherein the VF₂ content is about 18-60 mole % and the TFE/PMVE moleratio is 0.1-1.9. Preferably the VF₂ content is about 30-35 mole %, theTFE/PMVE mole ratio is about 0.2-0.3 and the substrate is PMMA.

In the case of the present invention the two-layer coating systemdeveloped for PMMA, PC, PET, and PS substrates comprises an upper layerselected from the group consisting of:

-   -   a) poly(TFE/HFP) and poly(VF₂/TFE/HFP), wherein the molar ratio        of TFE to HFP is between about 0.3 and 1.9 and, in the case of        the VF₂/TFE/HFP terpolymer, the concentration of VF₂ is about 19        mole %; and    -   b) poly(TFE/perfluoro-2,2-dimethyldioxole) wherein the        concentration of the perfluorodimethyldioxole is between 60 and        90 mole %;        and a lower coating layer selected from the group consisting of:    -   a) poly(VF₂/TFE/HFP) wherein the ratio of TFE to HFP is between        about 0.3 and 1.9 and the concentration of VF₂ is between about        18 and 60 mole % on PMMA substrates and between about 12 and 40        mole % on PC, PET, and PS substrates;    -   b) poly(VF/TFE/HFP) wherein the ratio of TFE to HFP is between        about 2.1 and 0.9 and the concentration of VF is between about        42 and 58 mole %;    -   c) poly(VAc/TFE/HFIB) wherein the concentration of VAc is        between, 36 and 69 mole % and the concentration of HFIB is        between 14 and 52 mole %; and    -   d) TFE graft to PVOH wherein about 46 mole % TFE has been        grafted to the PVOH.

More preferred is where the ratio of TFE to HFP is between about 0.9 and1.9 in both the lower and upper layer, and wherein the concentration ofVF₂ is between about 12 and 40 mole % when PC, PET, and PS substratesare utilized.

In the one layer coating system of the present invention, the thicknessof the coating is preferably between about 10 and 1000 nm, morepreferably, between about 30 and 120 nm, and most preferably betweenabout 70 and 120 nm.

In the two coat system, the thickness of the upper layer is preferablybetween 10 and 1000 nm. More preferably, it is between 30 and 120 nm andmost preferably, it is between 70 and 120 nm.

Another aspect of the invention is a new fluoropolymer compositionprepared by the polymerization of vinyl acetate (VAc, CH₃—C(O)—OCH═CH₂),tetrafluoroethylene (TFE, CF₂═CF₂), and hexafluoroisobutylene (HFIB,(CF₃)₂C═CH₂).

DETAILED DESCRIPTION OF THE INVENTION

Both one layer and two layer systems have been found that afford lowreflection coatings on optically clear plastic substrates. Preferredsubstrates are PMMA, PC, PET, and PS, and glass.

The one layer coating system provided by the present invention consistsof a fluorinated copolymer having the formula

VF₂/TFE/HFP

wherein the molar ratio of TFE to HFP is between 0.1 and 1.9 and the VF₂content is preferably 12 to 60 mole % for PMMA substrates and 18 to 60mole % for PC, PET, and PS substrates. These compositions balance thehigh fluorine content needed for low reflection, the high HFP contentneeded for optical clarity, and a sufficient VF₂ content to afford goodadhesion to the substrate. More preferred is where the molar ratio ofTFE to HFP is between 0.9 and 1.9, and the VF₂ content is preferably 12to 60 mole % for PMMA substrates and 18 to 60 mole % for PC, PET, and PSsubstrates. Also preferred is where the VF₂ content is 50 to 60 mole %for glass substrates.

Another embodiment of the one layer system comprises a fluorinatedcopolymer having the formula

VF₂/HFP

wherein the VF₂ is about 40-60 mole %. Preferably, the VF₂ content isabout 43 mole % and the substrate is PMMA.

Another embodiment of the one layer system comprises a fluorinatedcopolymer having the formula

VF₂/TFE/PMVE

wherein the VF₂ content is about 18-60 mole % and the TFE/PMVE moleratio is 0.1-1.9. Preferably the VF₂ content is about 30-35 mole %, theTFE/PMVE mole ratio is about 0.2-0.3 and the substrate is PMMA.

Although many polymers have a high enough fluorine content to performwell as a low reflection coating, they often fail because of inadequatebonding to substrates such as PMMA, PC, PET, and PS. This adhesionproblem has been solved by going to systems in which a lower adhesivecoat bonds a low-reflective top coat to the substrate. In the case ofthe present invention, the two-layer coating system developed for PMMA,PC, PET, and PS substrates consists of fluoropolymers having theformulas

Upper Coating Layer

-   -   Poly(TFE/HFP) and poly(VF₂/TFE/HFP), wherein the molar ratio of        TFE to HFP is between about 0.3 and 1.9 and, in the case of the        VF₂/TFE/HFP terpolymer, the concentration of VF₂ is about 19        mole %        -   or    -   poly(TFE/perfluoro-2,2-dimethyldioxole) wherein the        concentration of the perfluorodimethyldioxole is between 60 and        90 mole %

Lower Coating Layer

-   -   Poly(VF₂/TFE/HFP) wherein the ratio of TFE to HFP is between        about 0.3 and 1.9 and the concentration of VF₂ is between about        18 and 60 mole % on PMMA substrates and between about 12 and 50        mole % on PC, PET, and PS substrates        -   or    -   Poly(VF/TFE/HFP) wherein the ratio of TFE to HFP is between        about 2.1 and 0.9 and the concentration of VF is between about        42 and 58 mole %        -   or    -   Poly(VAc/TFE/HFIB) wherein the concentration of VAc is between        36 and 69 mole % and the concentration of HFIB is between 14 and        52 mole %        -   or    -   A TFE graft to PVOH wherein about 46 mole % TFE has been        grafted.

More preferred is where the ratio of TFE to HFP is between about 0.9 and1.9 in both the lower and upper layer, and wherein the concentration ofVF₂ is between about 12 and 40 mole % when PC, PET, and PS substratesare utilized.

The purpose of the lower layer in the present invention is to bondhighly-fluorinated, low-reflection polymers to higher-reflection,hydrocarbon-polymer substrates. In order to be an effective adhesiveagent, the polymer used for the adhesive layer combines perfluorocarbonmonomers such as TFE and HFP with either partially fluorinated orhydrocarbon comonomers such as VF₂, HFIB, and VAc.

In the one layer coating system of the present invention, the coatingneeds to be thicker than about 10 nm in order to observe a significantreduction in reflectivity. While thicknesses greater than 10 nm workwell, practical problems eventually arise as the coating is madethicker. For example, above about 1000 nm, thickness variation canbecome a problem, and, if the coating polymer is expensive, economicsstart to be prohibitive. Thus, in the one layer coating system of thepresent invention, the thickness of the coating is preferably betweenabout 10 and 1000 nm, more preferably, between about 120 and 300 nm,most preferably, between about 70 and 120 nm.

In the two layer coating system of the present invention the thicknessof the upper layer can be between 10 and 1000 nm. More preferably, it isbetween about 30 and 120 nm, most preferably between about 70 and 120nm. The coating process for the present invention can include anyprocess known in the art, including but not limited to dipping, spray,or spin coating method using polymer.

Another aspect of the invention is a new fluoropolymer compositionprepared by the copolymerization of vinyl acetate (VAc,CH₃—C(O)—OCH═CH₂), tetrafluoroethylene (TFE, CF₂═CF₂), andhexafluoroisobutylene (HFIB, (CF₃)₂C═CH₂). The polymer can be producedusing any free-radical polymerization method known in the art, includingbut not limited to bulk, solution or dispersion polymerization, usingeither nonaqueous or aqueous solvents. A preferred method is dispersionpolymerization. Preferred solvents are water and tert-butanol/methylacetate mixture. Dispersing agents can optionally be used; a preferredinitiator is Vazo®52. The polymer can further be hydrolyzed, partiallyor completely, to provide a vinyl alcohol containing copolymer.

The polymer can be recovered from the reaction using any conventionalprocedure such as filtration, followed by washing and drying. Thepolymer product can be readily dissolved in many solvents such asacetone and used for casting films and surface coatings having theadvantageous properties of fluoropolymers. One particular use is forpreparing coatings having low reflective properties.

The coatings can be prepared using any method known in the art. Suitablesolvents used for preparing the coatings are those which dissolve thecoating composition but are inert to the substrate being coated.Preferred solvents include fluorosolvents such as Fluorinert® (3MElectronic Materials, St. Paul, Minn.), Vertrel® (E. I. DuPont deNemours, Wilmington, Del.) or Novec® (3M Electronic Materials, St. Paul,Minn.), and ketone solvents such as methyl isobutyl ketone or acetone,isobutyl acetate, and combination of two or more thereof.

The following non-limiting Examples are meant to illustrate theinvention but are not intended to limit it in any way.

Materials and Methods

The following definitions are used herein and should be referred to forclaim interpretation.

-   -   APS—Ammonium persulfate    -   HFIB—Hexafluoroisobutylene, (CF₃)₂C═CH₂    -   HFP—Hexafluoropropylene, CF₂═CF—CF₃    -   PC—Polycarbonate    -   PET—Polyethyleneterephthalate    -   PMMA—Polymethylmethacrylate    -   PMVE—Perfluoromethylvinylether    -   PVOH—Polyvinyl alcohol    -   PS—Polysulfone    -   Teflon® AF—TFE/Perfluoro-2,2-dimethyldioxole copolymer    -   TFE—Tetrafluoroethylene, CF₂═CF₂    -   VAc—Vinyl acetate, CH₃—C(O)—OCH═CH₂    -   VF—Vinyl fluoride, CH₂═CHF    -   VF₂—Vinylidene fluoride, CF₂═CH₂        Unless otherwise indicated, the following test methods were        used:

Method of Measuring Transmission

Light transmission was measured at 500 nm using a Shimadzu #UV-3100Spectrometer. This machine measures a continuous comparison of a splitbeam, part of which passes through the sample.

Adhesion Test Method

A tool with 10 razor blades separated by a distance of 1 mm was used tocut the coating down to the plastic substrate, drawing the razor bladetool first in one direction and then a second time in a perpendiculardirection. This cuts 100 crosshatched squares. Scotch tape was appliedto the crosshatched area with moderate pressure and pulled off rapidly.Adhesion is scored as the number of squares out of 100 still attached tothe substrate.

VF2/TFE/HFP terpolymers and TFE/HFP copolymer having HFP contents inexcess of 30 mole % are perhaps most easily made by polymerization at14,000 psi and 200-400° C. as described in U.S. Pat. Nos. 5,478,905 and5,637,663. VF2/TFE/HFP terpolymers and the TFE/HFP dipolymers havinglower HFP contents as well as VF2/TFE/PMVE terpolymers can be run underordinary emulsion and bulk polymerization methods known in the art, seefor instance Encyclopedia of Polymer Science and Engineering, 1989, Vol.16, pg. 601-603 and Vol. 7, pg. 257-269, John Wiley & Sons.Non-crystalline compositions showing good optical clarity and easysolution coatability were then selected for this invention.

PVOH grafted with TFE was prepared as in U.S. Pat. No. 5,847,048, herebyincorporated by reference. The polymer contained about 46 mole % TFEgroups grafted to the vinyl alcohol.

The VAc/TFE/HFIB terpolymers were prepared as described in Examples 36to 45 below.

EXAMPLES Examples 1-9 Comparative Examples 1-3 One CoatPoly(VF₂/TFE/HFP) on PMMA Preferred Thickness Range

Solutions, 2 wt % poly(VF₂/TFE/HFP) in Fluorinert® FC-75, were made byagitating chunks of the polymer with solvent for several days at roomtemperature. PMMA plates measuring 2.5 cm by 5.0 cm by 3 mm thick wereused for testing. The PMMA plates were coated by lowering the platesinto the polymer solution at a rate of 300 mm/min. and then, 30 secondslater, raising the plates back out of the solution at 2.5 to 1000mm/min. After 5-10 minutes air drying, the plates were driedhorizontally for 60 minutes in a 100° C. air oven. Examples are in orderof increasing coating thickness.

TABLE 1 Single Coat of 18.7/43.3/38.0 mole % Poly(VF₂/TFE/HFP) on PMMAThickness (nm) Transmittance (%) Comp. #1 Uncoated PMMA control 92.1Comp. #2 5.0 92.8 Example #1 20.0 94.5 Example #2 70.6 96.7 Example #376.3 97.7 Example #4 90.2 98.0 Example #5 106.2 96.6 Example #6 133.393.2 Example #7 209.2 94.6 Example #8 394.7 95.2 Example #9 572.1 94.4Comp. #3 2000 not uniform

Uncoated PMMA showed 92.1% transmission. Coatings thicker than 20.0 nmand thinner than 1000 nm gave improved transmission (>93%) relative touncoated PMMA. The highest transmissions (>96%) were shown by coatings˜30 to 120 nm thick.

Examples 10-13 Comparative Examples 4-5 One Coat Poly(VF₂/TFE/HFP) onPMMA Preferred VF₂ Content

Polymer films were prepared as in Examples 1 to 9. Transmittance andadhesion were measured with the results shown in Table 2 below whichlists Examples and Comparative Examples in order of increasing VF₂content.

TABLE 2 Adhesion by Standard Tape Pull Test Single CoatPoly(VF₂/TFE/HFP) on PMMA Mole % Adhesion Transmittance VF₂/TFE/HFP(/100) (%) Comp. #1 Uncoated PMMA — 92.1 control Comp. #4 0/57/43Control 0 97.2 Comp. #5 7.8/60.3/31.8 64 97.5 Example #10 12.6/51.3/36.196 97.2 Example #11 18.7/43.3/38.0 99 97.9 Example #12 25.2/42.9/31.9100 95.1 Example #13 37.4/28.9/33.7 100 96.0

Simultaneous good adhesion (>96/100) and improved transmission (>97%)relative to uncoated PMMA were observed for VF₂/TFE/HFP polymers with 12to 50 mole % VF₂.

Example 14

A solution, 2 wt % poly(VF₂/TFE/HFP=46.9/13.5/39.6 mole %) in Vertrel®XF, were made by agitating chunks of the polymer with solvent forseveral days at room temperature. PMMA plates measuring 2.5 cm by 5.0 cmby 3 mm thick were used for testing. The PMMA plates were coated bylowering the plates into the polymer solution at a rate of 300 mm/min.and then, 30 seconds later, raising the plates back out of the solutionat 50 mm/min. After 5-10 minutes air drying, the plates were driedhorizontally for 60 minutes in a 100° C. air oven. Transmittance andadhesion were measured with the results shown the table below whichlists Examples.

TABLE 3 Single Coat of 46.9/13.5/39.6 mole % Poly(VF₂/TFE/HFP) on PMMAMole %'s Adhesion Transmittance VF₂TFE/HFP (/100) (%) Example46.9/13.5/39.6 100 97.4 #14B Comp. #1 Uncoated PMMA control — 92.1

Simultaneous good adhesion (100/100) and improved transmission (>97%)relative to uncoated PMMA were observed for VF₂/TFE/HFP=46.9/13.5/39.6mole % terpolymer.

Examples 15-18 Comparative Examples 6-8 Two Coats, Poly(VF₂/TFE/HFP) andPoly(HFP/TFE), on PMMA Preferred VF₂ Content

Solutions, 1 wt % poly(VF₂/TFE/HFP) with 0-40 mole % VF₂ in Fluorinert®FC-75, and with 4-55 mole % VF₂ in acetone were made by agitating chunksof the polymer with solvent for several days at room temperature. PMMAplates measuring 2.5 cm by 5.0 cm by 3 mm thick were used for testing.The PMMA plates were coated by lowering the plates into the polymersolution at a rate of 300 mm/min. and then, 30 seconds later, raisingthe plates back out of the solution at 50 mm/min. After 5-10 minutes airdrying, the plates were dried horizontally for 60 minutes in a 100° C.air oven. Examples and Comparative Examples are listed in order ofincreasing.

VF₂ content in the poly(VF₂/TFE/HFP) primer coat was varied. A 57 mole %TFE/43 mole % HFP top coat was used for all samples with apoly(VF₂/TFE/HFP) primer coat. Transmittance and adhesion were measuredwith the results shown in Table 4 below which lists the Examples andComparative Examples in order of increasing thickness.

TABLE 4 Two Coat, Poly(VF₂/TFE/HFP) and Poly(HFP/TFE) on PMMA PreferredVF₂ Content Mole % Adhesion Transmittance VF₂/TFE/HFP (/100) (%) Comp.#1 Uncoated PMMA control — 92.1 Comp. #4 0/57/43 Control 0 97.2 Comp. #67.8/60.3/31.8 0 97.7 Comp. #7 12.6/51.3/36.1 4 97.5 Example #1518.7/43.3/38.0 90 97.7 Example #16 49.3/27.7/23.0 100 97.3 Example #1752.0/25.9/22.1 98 97.5 Example #18 61.0/21.7/17.3 80 97.4 Comp. #866.2/16.9/16.9 6 97.1

Good adhesion with increased transmission relative to uncoated PMMAcontrol was observed when the poly(VF₂/TFE/HFP) primer layer had VF₂contents between about 18 and 60 mole %.

Examples 19-21 Two Coats Both Poly(VF₂/TFE/HFP) on PMMA TransmittanceIndependent of VF₂ Content of Primer Coat

Poly(VF₂/TFE/HFP) samples of different VF₂ content, see Table 5 below,were used for the primer coat. Solutions, 1 wt % poly(VF₂/TFE/HFP) inacetone, were made by agitating chunks of the polymer with solvent forseveral days at room temperature. PMMA plates measuring 2.5 cm by 5.0 cmby 3 mm thick were used for testing. The PMMA plates were coated bylowering the plates into the polymer solution at a rate of 300 mm/min.and then, immediately, raising the plates back out of the solution at 50mm/min. After 5-10 minutes air drying, the plates were driedhorizontally for 60 minutes in a 100° C. air oven. The topcoat, in everyinstance the same 18.7 mole % VF₂/43.3 mole % TFE/38.0 mole % HFPterpolymer, was prepared by the same method.

Table 5 below lists Examples and Comparative Examples in order ofincreasing VF₂ content.

TABLE 5 Two Poly(VF₂/TFE/HFP) Coats on PMMA Primer Coat Mole % AdhesionTransmittance VF₂/TFE/HFP (/100) (%) Comp. #1 Uncoated PMMA — 92.1Control Example 19 49.3/27.7/23.0 100 97.5 Example 20 61.0/21.7/17.3 10097.0 Example 21 66.2/16.9/16.9 100 97.5

In spite of variation in VF₂ content from 49.3 to 66.2 mole % in thelower layer, overall transmittance is relatively unaffected. Adhesion isexcellent (100/100) for VF₂ contents from 49.3 to 66.2 mole %.

Examples 22 to 24 Comparative Examples 9-12 One Coat Poly(VF₂/TFE/HFP)on Polycarbonate Preferred VF₂ Content

Poly(VF₂/TFE/HFP) terpolymer samples of different VF₂ content werecoated on polycarbonate (PC) sheet using the method of Example 14. Thepolycarbonate was manufactured by Kyoto-Jushi Seiko Co., Ltd. Thepolycarbonate sheets measured 2.5 cm×5.0 cm by 3 mm thick.

Transmission and adhesion were measured with the results shown in Table6 below which lists Examples and Comparative Examples in order ofincreasing VF₂ content.

TABLE 6 Single Poly(VF₂/TFE/HFP) Coat on PC Mole %'s AdhesionTransmittance VF₂/TFE/HFP (/100) (%) Comp. #9 Uncoated PC Control — 87.2Comp. #10 0/57/43 0 95.2 Comp. #11 7.8/60.3/31.8 0 90.5 Comp. #1212.6/51.3/36.1 53 94.7 Example #22 18.7/43.3/38.0 70 94.0 Example #2325.2/42.9/31.9 100 92.0 Example #24 37.4/28.9/33.7 100 93.8

VF₂ contents between about 18 and 40 mole % give improved adhesion(>70/100) relative to HFP/TFE copolymer (0/100) and improvedtransmission (>92%) relative to uncoated PC (87.2%).

Examples 25-28 Comparative Examples 13 to 14 Two Coats on PolycarbonatePreferred VF₂ Content for Primer

Poly(VF₂/TFE/HFP) samples of different VF₂ content, see Table 7 below,were used for the primer coat. Solutions, 1 wt % poly(VF₂/TFE/HFP) inacetone, were made by agitating chunks of the polymer with solvent forseveral days at room temperature. PC plates (Kyoto-Jushi Seiko Co.,Ltd.) measuring 2.5 cm by 5.0 cm by 3 mm thick were used for testing.The PC plates were coated by lowering the plates into the polymersolution at a rate of 300 mm/min. and then, immediately, raising theplates back out of the solution at 50 mm/min. After 5-10 minutes airdrying, the plates were dried horizontally for 60 minutes in a 100° C.air oven.

The topcoat, in every instance the same 57.0 mole % TFE/43.0 mole % HFPcopolymer, was prepared by the same method.

Table 7 below lists Examples and Comparative Examples in order ofincreasing VF₂ content.

TABLE 7 Two Coats on PC Primer Coat Mole % Adhesion TransmittanceVF₂/TFE/HFP (/100) (%) Comp. #9 Uncoated PC — 87.2 control Comp. #130/57/43 control 68 93.8 Comp. #14 7.8/60.3/31.8 12 91.6 Example #2512.6/51.3/36.1 83 94.2 Example #26 18.7/43.3/38.0 96 92.3 Example #2725.2/42.9/31.9 88 93.4 Example #28 37.4/28.9/33.7 97 93.2

VF₂ contents between about 12 and 40 mole % give improved adhesion(>83/100) relative to HFP/TFE dipolymer (68/100) and improvedtransmittance (>92.3%) relative to uncoated polycarbonate (87.2%).

Examples 29 to 31 Two Coats on PMMA Use of Poly(VF/TFE/HFP) as PrimerCoat Preferred VF Content

A stirred jacketed stainless steel horizontal autoclave of 7.6 L (2 U.S.gal) capacity was used as the polymerization vessel. The autoclave wasequipped with instrumentation to measure temperature and pressure andwith a compressor that could feed monomer mixtures to the autoclave atthe desired pressure. The autoclave was filled to 55-60% of its volumewith deionized water containing 15 g of Zonyl® FS-62 surfactant (E.I.DuPont de Nemours, Wilmington, Del.?) and heated to 90° C. It was thenpressured to 3.1 MPa (450 psig) with nitrogen and vented three times.The autoclave was precharged with monomers in the desired ratio, asshown in the table below, and brought to the working pressure of 3.1 MPa(450 psig). Initiator solution was prepared by dissolving 2 g APS in 1 Lof deionized water. The initiator solution was fed to the reactor at arate of 25 mL/min for a period of five minutes and then the rate wasreduced and maintained at 1 mL/min for the duration of the experiment.For Examples 36 and 38 the autoclave was operated in a batch mode. Thepolymerization was terminated after a 10% pressure drop was observed byventing the remaining unconverted monomers and by reducing the autoclavetemperature to room temperature.

For the 26.2/46.4/27.5 polymer, the autoclave was operated in asemibatch fashion in which a monomer mixture was added to the reactor tomaintain constant pressure by means of the compressor as polymerizationoccurred. The composition of this make-up feed was different from theprecharged mixture, as shown in the table below, because of thedifferences in monomer reactivity. The composition was selected tomaintain a constant monomer composition in the reactor socompositionally homogeneous product was formed. Make-up monomer feed wasadmitted to the autoclave, through the compressor, by means of anautomatic pressure regulated valve to maintain reactor pressure. Monomerfeeds were continued until a predetermined amount to give the finallatex solids was fed to the autoclave. The feed was then stopped and thecontents of the autoclave were cooled and vented.

In all cases, the polymer latex was easily discharged to a receiver as amilky homogeneous mixture. Polymer was isolated on a suction filterafter adding 15 g of ammonium carbonate dissolved in water per liter oflatex followed by 70 mL of HFC-4310(1,1,1,2,3,4,4,5,5,5-decafluoropentane) per liter of latex with rapidstirring. The filter cake was washed with water and dried in an air overat 90-100° C.

TABLE 8 Monomer Monomer Mono- Polymer Precharge Make-up mer Comp.TFE/VF/ TFE/VF/ Fed Solids Polymer TFE/VF/HFP HFP (wt %) HFP (wt %) (g)(wt %) (g) (wt %) 15/3/82 750.9 2.1 96.6 38.3/42.8/19 9/3/88 29/46/251702 18.3 1063 26.2/46.4/27.5 10/10/80 636.1 2.2 99.7 20.3/57.8/22

Poly(VF/TFE/HFP) samples of different VF content, see Table 9 below,were used for the primer coat. Solutions, 2 wt % poly(VF/TFE/HFP) inacetone, were made by agitating chunks of the polymer with solvent forseveral days at room temperature. PMMA plates measuring 2.5 cm by 5.0 cmby 3 mm thick were used for testing. The PMMA plates were coated bylowering the plates into the polymer solution at a rate of 300 mm/min.and then, immediately, raising the plates back out of the solution at 50mm/min. After 5-10 minutes air drying, the plates were driedhorizontally for 60 minutes in a 100° C. air oven.

The topcoat, in every instance the same 57 mole % TFE/43 mole % HFPpolymer, was prepared by the same method.

Table 9 below lists Examples in order of increasing VF content.

TABLE 9 Two Coats, VF/TFE/HFP Primer, on PMMA Primer Coat Mole %'sAdhesion Transmittance VF/TFE/HFP (/100) (%) Comp. #1 Uncoated PMMA —92.1 control Example #29 42.8/38.3/19.0 99 96.3 Example #3046.4/26.2/27.5 100 97.3 Example #31 57.8/20.8/22.0 100 96.0

For VF contents from about 42 to 58 mole %, use of poly(VF/TFE/HFP) asthe primer coat gives excellent transmittance (>96.0%) relative touncoated PMMA (92.1%) along with excellent adhesion (>99/100).

Example 32 Two Coats on PMMA Use of Graft of TFE to PVOH as Primer Coat

A poly(vinyl alcohol) to which 46 mole % TFE had been grafted(PVOH-g-TFE) was used for the primer coat. A solution, 2 wt % inacetone, was made by agitating chunks of the polymer with solvent forseveral days at room temperature. PMMA plates measuring 2.5 cm by 5.0 cmby 3 mm thick were used for testing. The PMMA plates were coated bylowering the plates into the polymer solution at a rate of 300 mm/min.and then, immediately, raising the plates back out of the solution at 50mm/min. After 5-10 minutes air drying, the plates were driedhorizontally for 60 minutes in a 100° C. air oven.

The topcoat, an 57 mole % TFE/43 mole % HFP polymer, was prepared by thesame method.

Table 10 below gives adhesion and transmission results.

TABLE 10 Two Coats, PVOH-g-TFE Primer, on PMMA Primer Coat AdhesionTransmittance PVOH-g-TFE (/100) (%) Comp. #1 Uncoated PMMA control —92.1 Example #32 46 mole % TFE 97 97.1

Use of poly(PVOH-g-TFE) as the primer coat gave excellent transmittance(97.1%) relative to uncoated PMMA (92.1%) along with excellent adhesion(97/100).

Example 33 Comparative Examples 15-16 One Coat Poly(VF₂/TFE/HFP) on PET

Coatings were prepared as in Examples 1 to 9. PET sheets measuring 2.5by 5.0 cm by 0.12 mm thick were used as substrate. Transmittance andadhesion were measured with the results shown in the table below whichlists Examples and Comparative Examples.

TABLE 11 Poly(VF₂/TFE/HFP) Coat on PET Mole %'s Adhesion TransmittanceVF₂/TFE/HFP (/100) (%) Comp. #15 Uncoated PET control — 85.0 Comp. #160/57/43 2 96.0 Example #33 18.7/43.3/38.0 99 96.0

Uncoated PET showed 85.0% transmission. Simultaneous good adhesion(>99/100) and improved transmission (>96%) relative to uncoated PET wereobserved.

Example 34 Comparative Example 17-18 One Coat Poly(VF₂/TFE/HFP) onPolysulfone

Coatings were prepared as in Example 1 to 9. Polysulfone sheetsmeasuring 2.5×5.0 cm by 0.05 mm thick were as substrate. Transmittanceand adhesion results are shown in the table below which lists Examplesand Comparative Examples.

TABLE 12 Single Coat Poly(VF₂/TFE/HFP) on Polysulfone Mole %'sVF₂/TFE/HFP Adhesion (/100) Transmittance (%) Comp. #17 Uncoated PS —88.5 Comp. #18 0/57/43 97 98.2 Example #34 18.7/43.3/38.0 100 95.0

Uncoated polysulfone showed 88.5% transmittance. Simultaneous goodadhesion (>97/100) and improved transmission (>95%) relative to uncoatedpolysulfone (88.5%) were observed.

Example 35 Comparative Example 19

Two coat polymer films were prepared on PMMA sheet as in Examples 15-18.A Teflon® AF top coat was used. Transmittance and adhesion were measuredwith the results shown in the table below which lists the Examples andComparative Examples.

TABLE 13 Two Coats, Poly(VF₂/TFE/HFP) and Teflon ® AF, on PMMA Mole %'sAdhesion Transmittance VF₂/TFE/HFP (/100) (%) Comp. #1 Uncoated PMMAcontrol — 92.1 Comp. #19 AF1600 control (no lower 0 98.1 coat) Example#35 49.3/27.7/23.0 100 98.0

Adhesion was 100/100 for the two coat sheet (VF₂/TFE/HFP and Teflon® AF)but only 0/100 for the sheet with a single coating of Teflon® AF. Thisshows that poly(VF₂/TFE/HFP) is an effective primer that furtherimproves the adhesion of Teflon® AF.

Transmittance at 500 nm was 98.0% for two coat sheet (VF₂/TFE/HFP andAF) but only 92.1 for uncoated PMMA control. This shows that Teflon® AFis an effective top coat that further improves the transmittance ofpoly(VF₂/TFE/HFP).

Examples 36-45

Aqueous Polymerization of VAc/TFE/HFIB. A 1-L stirred vertical autoclavewas charged with a solution of 0.3 g of Plasdone K-90 (stericstabilizer) and 5 mL isopropanol (chain transfer agent) in 400 mL ofdeionized water. Vinyl acetate (126 g, 1.47 mole) and 0.6 g of Vazo® 52were added. The vessel was closed, pressurized to 100 psi with nitrogenand vented twice. The vessel was pressured to 295 psi with nitrogen as aleak test and vented. The vessel was cooled to about −4° C., evacuatedand charged with 42 g (0.26 mol) of hexafluoroisobutylene and 42 g (0.42mol) of tetrafluoroethylene. With stirring at 750 rpm, the vesselcontents were heated to 70° C. and maintained for 3 hr. The contents washeated to 85° C. and maintained for 3 hr. After cooling to roomtemperature and venting to atmospheric pressure, the aqueous suspensionwas removed from the vessel using water as necessary to rinse. Anadditional 350 mL of deionized water were added and the white suspensionwas heated with stirring on a hot plate until about 250 mL of solutionhad evaporated. After cooling to room temperature, the solid was easilyfiltered on a sintered glass funnel and washed with deionized water. Itwas dried in a vacuum oven at 90° C. overnight giving 181.8 g (87%) ofwhite polymer.

Nonaqueous Polymerization of VAc/TFE/HFIB. A 1-L stirred verticalautoclave was charged with a solution of 126 g of vinyl acetate in 110 gof methyl acetate and 200 g of tert-butanol. The vessel was closed,pressurized to 100 psi with nitrogen and vented twice. The vessel waspressured to 295 psi with nitrogen as a leak test and vented. The vesselwas cooled to about −4° C., evacuated and charged with 63 g oftetrafluoroethylene and 21 g of HFIB. With stirring at 750 rpm, thevessel contents were heated to 70° C. A solution (25 mL) of 0.2 g Vazo®52 in 25 mL methyl acetate was injected at 5 ml/min. After 3 hr. thevessel contents were allowed to cool to room temperature and theremaining gases were vented. The viscous solution was removed from thevessel by suction, diluting with acetone as necessary to lower solutionviscosity. The polymer solution, further diluted with acetone ifnecessary to give a clear solution, was added slowly in 30-45 mLportions to 16 oz of deionized water and a small amount of ice in ablender. The precipitated solid was filtered in a sintered glass funnel.After all polymer had been precipitated the combined solids were washedin portions with water, filtered and pressed with a rubber dam. Thesolid was dried for several hours in a vacuum oven with a slow nitrogenpurge at 110-115° C. The resulting white solid weighed 141.1 g (67%).

Table 14 below gives results for polymerizations carried out by one ofthe methods listed above.

Vinyl acetate content was determined by hydrolysis of the acetate groupsusing excess of sodium hydroxide in refluxing THF, followed by titrationof excess base by standard hydrochloric acid solution. GPC analyses wereconducted using THF as solvent and polystyrene standards. Elementalanalyses were done by Schwarkkoff Microanalytical Laboratory. ¹⁹F NMRspectra were generally measured in THF-d6 solutions using TMS and CFC-11as internal standards. ¹⁹F NMR was used to assign relative amounts ofthe two fluorinated monomers from integration of the CF₃ groups of HFIBat −66 to −70 versus the CF₂ groups from TFE at −110 to −126.

TABLE 14 Monomers Weight Ratio Polym. g, Yield Wt. % F NMR RefractiveInh. GPC Ex. (g) Feed/(Product^(a)) Solv.^(b) Reactor (%) VAc (mole %)Index Visc. % F^(c) Mw/Mn/PD 36 VAc (52) 40:23:37 t-BuOH 400 mL  94.6(72) 39.0 TFE 31% 1.4111 0.41 38.92 148,000 TFE (30) (39:13:48) MeAcHFIB 69% 84,900 HFIB (49) 1.75 37 VAc (86) 39:23:38 Water 1 L 175.6 (81)35.5 TFE 28% 1.4169 0.38 36.70 177,000 TFE (50) (36:12:52) PVP HFIB 72%82,500 HFIB (82) 2.15 38 VAc (103) 49:19:32 Water 1 L 182.5 (87) 50.2TFE 33% 1.4191 0.52 31.09 252,000 TFE (40) (50:12:38) PVP HFIB 67%81,800 HFIB (66) 3.08 39 VAc (126) 60:20:20 Water 1 L 181.8 (87) 58.1TFE 50% 1.4307 0.79 22.95 349,000 TFE (42) (58:16:26) PVP HFIB 50%120,000 HFIB (42) 2.90 40 VAc (126) 60:30:10 Water^(d) 1 L 172.9 (82)68.6 TFE 73% 1.4368 1.98 20.83 786,000 TFE (63) (69:19:12) PVP HFIB 27%208,000 HFIB (21) 3.77 41 VAc (147) 70:20:10 Water^(d) 1 L 186.3 (89)70.7 TFE 66% 1.4439 2.01 17.69 857,000 TFE (42) (71:16:13) PVP HFIB 34%243,000 HFIB (21) 3.52 42 VAc (126) 60:30:10 t-BuOH 1 L 141.1 (67) 61.5TFE 74% 1.4284 0.78 26.22 235,000 TFE (63) (62:24:14) MeAc HFIB 26%100,000 HFIB (21) 2.33 43 VAc (126) 60:20:20 t-BuOH 1 L 148.4 (71) 57.2TFE 48% 1.4198 0.59 29.83 204,000 TFE (42) (57:15:27) MeAc HFIB 52%116,000 HFIB (42) 1.76 44 VAc (147) 70:20:10 t-BuOH 1 L 142.5 (68) 66TFE 68% 1.4353 0.78 22.33 230,000 TFE (42) (66:19:15) MeAc HFIB 32%126,000 HFIB (21) 1.82 45 VAc (147) 70:20:10 Water 1 L 187.1 (89) 68.8TFE 68% 1.4422 1.09 17.83 437,000 TFE (42) (69:17:14) PVP HFIB 32%145,000 HFIB (21) 3.0 ^(a)Vinyl acetate content determined by hydrolysisof the acetate groups using standard base, fluoromonomer incorporationwas determined by ¹⁹F NMR. ^(b)Polyvinyl pyrrolidone (0.3 g) used asdispersing agent and isopropanol (5 mL) used as chain transfer agent inaqueous polymerizations. ^(c)Elemental analysis ^(d)No chain transferagent used.

Examples 46-48 Two Coats on PMMA Use of Poly(VAc/TFE/HFIB) as PrimerCoat Preferred VAc Content

Poly(VAc/TFE/HFIB) samples of different VAc content, see Table 15 below,were used for the primer coat. Solutions, 2 wt % poly(VAc/TFE/HFIB) inacetone, were made by agitating chunks of the polymer with solvent forseveral days at room temperature. PMMA plates measuring 2.5 cm by 5.0 cmby 3 mm thick were used for testing. The PMMA plates were coated bylowering the plates into the polymer solution at a rate of 300 mm/min.and then, immediately, raising the plates back out of the solution at 50mm/min. After 5-10 minutes air drying, the plates were driedhorizontally for 60 minutes in a 100° C. air oven.

The topcoat, in every instance the same 57 mole % TFE/43 mole % HFPpolymer, was prepared by the same method.

Table 15 below lists Examples and in order of increasing VAc content.

TABLE 15 Two Coats, VAc/TFE/HFIB Primer, on PMMA Primer Coat Mole %Adhesion Transmittance VAc/TFE/HFIB (/100) (%) Comp. #1 Uncoated PMMAcontrol — 92.1 Example #46 36/12/52 100 96.8 Example #47 58/16/26 10097.6 Example #48 69/17/14 100 97.3

For VAc contents from about 36 to 69 mole %, use of poly(VAc/TFE/HFIB)as the primer coat gives excellent transmittance (>96.8%) relative touncoated PMMA (92.1%) along with excellent adhesion (100/100).

Examples 49-55 Comparative Examples 20-23

Solutions of 2.5 wt % poly(VF2/TFE/HFP) in Novec® HFE-7100 (3MElectronic Materials, St. Paul, Minn.) and poly(TFE/HFP) in Fluorinert®(3M Electronic Materials, St. Paul, Minn.) FC-75, were made by agitatingchunks of the polymer with solvent for several days at room temperature.PMMA and PC plates measuring 2.5 cm by 5.0 cm by 3 mm thick, PET filmsmeasuring 2.5 cm by 5.0 cm by 120 micron meter thick and glass plates2.5 cm by 5.0 cm by 1 mm thick were used for testing. The plates werecoated by lowering the plates into the polymer solution at a rate of 300mm/min. and then, 30 seconds later, raising the plates back out of thesolution at 125 mm/min. After 5-10 minutes air drying, the plates weredried for 10 minutes in an air oven. The temperature was 100° C. forPMMA, 120° C. for PC and 300° C. for glass plates. The PET films weredried for 60 minutes in a 100° C. air oven. Transmittance, adhesion andcoating thickness were measured with the results shown in Table 16.

TABLE 16 Example #49 Example #50 Example #51 Example #52 Example #53Example #54 VF2 (mol %) 48 50 52 57 50 50 HFP (mol %) 45 23 22 34 23 23TFE (mol %)  7 27 26  9 27 27 Substrate PMMA PMMA PMMA PMMA PC PETThickness 90 90 90 90 90 90 (nm) Adhesion 100  100  100  100  100  100 (/100) Transmittance 97 98 97 97 95 97 (%) Example #55 Comp. #20 Comp.#21 Comp. #22 Comp. #23 Comp. #24 VF2 (mol %) 50 — — — —  0 HFP (mol %)23 — — — — 43 TFE (mol %) 27 — — — — 57 Substrate Glass PMMA PC PETGlass PMMA Thickness 90 Uncoated Uncoated Uncoated Uncoated 90 (nm)Adhesion 100  — — — —  0 (/100) Transmittance 96 92 87 90 90 97 (%)

Simultaneous good adhesion (>96/100) and improved transmittance (>95%)relative to uncoated substrates were observed for VF2/TFE/HFP polymerswith 40 to 60 mole % VF2.

Examples 56-57

Solutions, 2.5 wt % poly(VF2/HFP=43/57 mole %) in Vertrel® XF (E. I.DuPont de Nemours, Wilmington, Del.) and poly(VF2/HFP=78/22 mole %) inMIBK, were made by agitating chunks of the polymer with solvent forseveral days at room temperature. PMMA plates measuring 2.5 cm by 5.0 cmby 3 mm thick and glass plates 2.5 cm by 5.0 cm by 1 mm thick were usedfor testing. Polymer films were prepared as in Examples 49 to 55 with athickness of 90 nm Lifting up speed was 200 mm/min. Transmittance andadhesion were measured with the results shown in Table 17.

TABLE 17 Example #56 Example #57 VF2 (mol %) 43 78 HFP (mol %) 57 22Substrate PMMA Glass Adhesion(/100) 100  100  Transmittance(%) 95 95

Simultaneous good adhesion (>96/100) and improved transmittance (>95%)relative to uncoated PMMA and glass were observed for VF2/HFP polymerswith 40 to 80 mole % VF2.

Example 58

Solutions, 3 wt % poly(VF2/TFE/PMVE=32/15/53 mole %) in Novec® HFE-7200(3M Electronic Materials, St. Paul, Minn.) were made by agitating chunksof the polymer with solvent for several days at room temperature. PMMAplates measuring 2.5 cm by 5.0 cm by 3 mm thick were used for testing.Polymer films were prepared as in Examples 1 to 7. Lifting up speed was75 mm/min. Transmittance and adhesion were measured with the resultsshown in Table 18.

TABLE 18 Example #58 VF2 (mol %) 32 TFE (mol %) 15 PMVE (mol %) 53Substrate PMMA Adhesion (/100) 100  Transmittance (%) 98

Simultaneous good adhesion (>96/100) and improved transmittance (>95%)relative to uncoated PMMA were observed.

1-12. (canceled)
 13. A composition prepared by the polymerization ofvinyl acetate (VAc, CH₃—C(O)—OCH═CH₂), tetrafluoroethylene (CF₂═CF₂),and hexafluoroisobutylene ((CF₃)2C═CH₂). 14-23. (canceled)